Abstract
Continuous social isolation (SI) from an early developmental stage may have different effects in youth and adulthood. Moreover, SI is reported to impair neuronal plasticity. In this study, we used post-weaning rats to compare the impact of continuous SI on depressive-like, anxiety-related, and fear-related behaviors and neuronal plasticity in puberty and adulthood. Furthermore, we assessed the effect of lithium on behavioral changes and neuronal plasticity. Continuous SI after weaning induced depressive-like behaviors in puberty; however, in adulthood, depressive-like and anxiety-related behaviors did not increase, but—paradoxically—decreased in comparison with the controls. The decreased expression of neuronal plasticity-related proteins in the hippocampus in puberty was more prominent in the prefrontal cortex and hippocampus in adulthood. In contrast, SI after weaning tended to decrease fear-related behaviors in puberty, a decrease which was more prominent in adulthood with increased neuronal plasticity-related protein expression in the amygdala. Lithium administration over the last 14 days of the SI-induced period removed the behavioral and expression changes of neuronal plasticity-related proteins observed in puberty and adulthood. Our findings suggest that the extension of the duration of SI from an early developmental stage does not simply worsen depressive-like behaviors; rather, it induces a behavior linked to neuronal plasticity damage. Lithium may improve behavioral changes in puberty and adulthood by reversing damage to neuronal plasticity. The mechanisms underlying the depressive-like and anxiety-related behaviors may differ from those underlying fear-related behaviors.
Highlights
Depression is a common mood disorder that raises major public health concerns (Smith 2014) and is influenced by several social problems
As the main purpose of this study, we evaluated the influence of continuous social isolation (SI) on depressive-like and anxiety-related behaviors in puberty and adulthood in post-weaning rats
In searching for a way to treat unstable moods associated with continuous SI from an early age, we investigated the effect of lithium on the behavioral changes and neuronal plasticity
Summary
Depression is a common mood disorder that raises major public health concerns (Smith 2014) and is influenced by several social problems. The relationship between social isolation (SI) and depression has been well investigated. SI has been shown to be associated with. SI can happen in adulthood (after puberty or adolescence) but from an early developmental age as well (after weaning or in early childhood). Depression in youth, i.e., during puberty or adolescence, has attracted attention, and either SI or insufficient attachment in early developmental stages is thought to be related to the onset of depression in puberty or adolescence (Ford and Rechel 2012; Shaw and Dallos 2005). An experiment using animals reported that the limitations of maternal attachment from postnatal day (P) 8 to P12 induced depressive-like behaviors in puberty (Raineki et al 2012).
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